In an iron bath-type melting furnace, molten iron is produced by melting an iron source material through combustion of carbon in molten pig iron and/or a carbonaceous material supplied into the furnace with blowing of oxygen. Methods for taking the molten iron stored in the furnace to outside include batch methods and continuous methods. Both methods, however, have still the below-described problems, and there is as yet no established method.
(Conventional Technology 1)
Numerous methods using a converter-type furnace as iron bath-type melting furnace have been proposed (e.g., refer to Patent document 1). However, the method using a converter-type furnace as iron bath-type melting furnace must stop oxygen blowing (i.e., stop production of the molten iron) and tilt the furnace body to discharge molten iron and molten slag (hereinafter may be simply referred to as “slag”). The stop of blowing poses a problem in that the productivity of molten iron is reduced. In addition, the thermal loss from the surface of the furnace body to its outside air in discharging the molten iron decreases the temperature of melt in the furnace, therefore, the method needs a temperature-raising operation to recover the drop of melt's temperature before charging the iron source material until the next blowing starts. This operation poses a problem in that the productivity of molten iron is further reduced.
(Conventional Technology 2)
On the other hand, a continuous molten iron discharge-type melting furnace as iron bath-type melting furnace has been disclosed (refer to Patent document 2). The furnace has: a discharge port of molten iron and slag formed in a side of the furnace bottom; a refractory structure, which is called forehearth, provided at the front face of the discharge port of molten iron and slag; and a channel for continuous discharge of molten iron, which runs from the discharge port of molten iron and slag up to a molten iron discharge position in a molten iron discharge trough, formed inside the refractory structure (i.e., forehearth). However, the thermal loss between the forehearth and the molten iron discharge trough is large in this continuous molten iron discharge-type melting furnace, and the method using this furnace needs heating by an auxiliary burner or the like. Moreover, when oxygen blowing is discontinued on account of equipment malfunction arising from, for instance, the raw material supply equipment or the oxygen supply equipment, the method poses a problem in that molten iron or molten slag solidify and clog between the forehearth and the molten iron discharge trough and that its repair work requires tremendous amounts of time and money. Besides, molten iron is discharged not batch-wise but continuously in this method. As a result, it takes time for a ladle to receive the required amount of molten iron used in a subsequent steel making process, which is a batch process. The drop of temperature of the molten iron discharged initially is herein non-negligible, and, in the worst case, the molten iron may end up solidifying in the ladle.    Patent document 1: Japanese Examined Patent Application Publication No. H3-49964    Patent document 2: Japanese Patent Application Publication No. 2001-303114